strtok_r(3)                Library Functions Manual                strtok_r(3)

NAME
       strtok_r - string tokenize reentrant

LIBRARY
       Standard C library (libc, -lc)

SYNOPSIS
       #include <string.h>

       char *strtok_r(char *_Nullable restrict str, const char *restrict delim,
                      char **restrict saveptr);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       strtok_r():
           _POSIX_C_SOURCE
               || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

DESCRIPTION
       The strtok_r() function is a reentrant version of strtok(3).

       The saveptr argument is a pointer to a char * variable that is used
       internally by strtok_r() in order to maintain context between
       successive calls that parse the same string.

       On the first call to strtok_r(), str should point to the string to be
       parsed, and the value of *saveptr is ignored (but see VERSIONS).  In
       subsequent calls, str should be NULL, and saveptr (and the buffer that
       it points to) should be unchanged since the previous call.

       Different strings may be parsed concurrently using sequences of calls
       to strtok_r() that specify different saveptr arguments.

RETURN VALUE
       strtok_r() returns a pointer to the next token, or NULL if there are no
       more tokens.

ATTRIBUTES
       For an explanation of the terms used in this section, see
       attributes(7).

       +--------------------------------------------+---------------+---------+
       |Interface                                   | Attribute     | Value   |
       +--------------------------------------------+---------------+---------+
       |strtok_r ()                                 | Thread safety | MT-Safe |
       +--------------------------------------------+---------------+---------+
VERSIONS
       On some implementations, *saveptr is required to be NULL on the first
       call to strtok_r() that is being used to parse str.

STANDARDS
       POSIX.1-2008.

HISTORY
       POSIX.1-2001.

EXAMPLES
       The program below uses nested loops that employ strtok_r() to break a
       string into a two-level hierarchy of tokens.  The first command-line
       argument specifies the string to be parsed.  The second argument
       specifies the delimiter byte(s) to be used to separate that string into
       "major" tokens.  The third argument specifies the delimiter byte(s) to
       be used to separate the "major" tokens into subtokens.

       An example of the output produced by this program is the following:

           $ ./a.out 'a/bbb///cc;xxx:yyy:' ':;' '/'
           1: a/bbb///cc
                    --> a
                    --> bbb
                    --> cc
           2: xxx
                    --> xxx
           3: yyy
                    --> yyy

   Program source
       #include <stdio.h>
       #include <stdlib.h>
       #include <string.h>

       int
       main(int argc, char *argv[])
       {
           char *str1, *str2, *token, *subtoken;
           char *saveptr1, *saveptr2;
           int j;

           if (argc != 4) {
               fprintf(stderr, "Usage: %s string delim subdelim\n",
                       argv[0]);
               exit(EXIT_FAILURE);
           }

           for (j = 1, str1 = argv[1]; ; j++, str1 = NULL) {
               token = strtok_r(str1, argv[2], &saveptr1);
               if (token == NULL)
                   break;
               printf("%d: %s\n", j, token);

               for (str2 = token; ; str2 = NULL) {
                   subtoken = strtok_r(str2, argv[3], &saveptr2);
                   if (subtoken == NULL)
                       break;
                   printf("\t --> %s\n", subtoken);
               }
           }

           exit(EXIT_SUCCESS);
       }

SEE ALSO
       strtok(3)

Linux man-pages 6.19              2026-02-25                       strtok_r(3)